|  | Conditions Treatments | Ears Hearing

Explanation of Air Conduction Masking

Humans hear sounds in two ways, bone conduction through the bones around the ear and air conduction of sound waves traveling through the inner ear to the bones of the middle ear. An audiometry hearing test for air conduction involves wearing earphones on each ear. To ensure a proper test result, the technique of masking is employed.

  1. Procedure

    • Sound waves travel through the air and enter the ear. They move from the inner ear to the ear canal and eardrum. They then reach the middle ear. The test for this process involves sending a sound through one of the two earphones worn by the subject. The purpose is to test hearing in each ear. A problem with the test involves the fact that one ear can be incapable of hearing the sound but the other ear picks it up. Masking is the technique to eliminate that problem.

    Sound Level

    • Decibels, or db, represent the unit of measurement for sound intensity. For example, a whisper is 20 db, while a jet engine registers 140 to 180 db. When performing an air conduction test, masking is utilized at 40 db or higher. This eliminates the so-called crossover problem of a good ear "masking" the faults of a bad ear.

    Technique

    • Masking is a technique that places noise in one ear while sending a sound to the other ear. The noise "masks" the sound in the other ear so there can be no question that the subject either hears or does not hear the sound. The good ear cannot compensate for the bad ear. Masking is always needed where one ear hears better than the other. If both ears had equal ability, masking would not matter.

    Problem

    • A problem with masking involves the person with moderate to severe hearing loss. Moderate hearing loss means a person cannot hear tones from 41 db to 55 db at least 50 percent of the time. A person with this hearing loss will have trouble with conversational speech. When tested using masking, the noise is too loud and drowns out the testing sound. The use of insert earphones sometimes solves the problem. If not, then another type of testing is required.

Ears Hearing - Related Articles